The present invention relates to an ultrasonic diagnostic apparatus for obtaining a topographic image with respect to a diagnostic portion of the body to be inspected by utilizing an ultrasonic wave, and more particularly to an ultrasonic diagnostic apparatus in which the motion of a moving portion such as a heart, a blood vessel and a blood stream in a body to be inspected can be depicted with colored differential images without using a contrast medium and a series of images of the moving portion can also be displayed on a scope.
B mode display, Doppler mode display and the like have been known as a method of displaying images of the blood stream, the heart and the like in the body to be inspected in real time by using an ultrasonic wave. An attempt to obtain differential images with ultrasonic topographic images is discussed in British Heart Journal 59 (1988) pp. 12-19. In this technique, a contrast medium is used and subtraction is made between topographic images before and after injection of the contrast medium so that observation may be made with contrast formed of a region of a heart for instance.
For example, in this method of image display, four frames of ultrasonic topographic images are taken before injecting the contrast medium into a body to be inspected and these four frames of images are added and averaged to form a mask image A as shown in FIG. 1. Then a contrast medium is injected into the body and topographic images (B.sub.1, B.sub.2, . . . B.sub.n) are taken after a lapse of time to allow the contrast medium to reach a portion of the body to be diagnosed, and subtraction is made between the mask image and respective topographic images after injection of the contrast medium so as to obtain differential images (C.sub.1, C.sub.2, . . . , C.sub.n) in consecutive order. Namely, the differential images are obtained in such a manner that B.sub.1 -A=C.sub.1, B2-A=C.sub.2, . . . B.sub.n -A=C.sub.n. In this method, the density of respective picture elements in the image which becomes the mask image is a mean value of the density of corresponding picture elements of the four frames. This method obtains better differential images by reducing effects of random noise affecting the differential images.
Further, an ultrasonic diagnostic apparatus which displays differential images is described in the 55th Proceeding of the Japan Society of Ultrasonics in Medicine (issued on Oct. 4, 1989) pp. 291-292, and in the 56th Proceeding of the Japan Society of Ultrasonics in Medicine (issued in May, 1980) pp. 351-354. Further, display of differential images in these ultrasonic diagnostic apparatus is made in such a manner that differentiation is obtained among tomographical images in a time series with the differential images being displayed one by one in consecutive order.
In the case of image display by such a conventional ultrasonic diagnostic apparatus, a contrast medium is injected into the blood of the patient so as to depict a location where blood is moving such as the ventricle and atrium by emphasizing the contrast. Therefore, it has been difficult to obtain movement information of a portion of the patient's body having small blood stream such as a tissue itself. Further, although the movement of an inner wall of a ventricle or atrium can be observed, the movement of the outer wall cannot be observed. Furthermore, since a contrast medium is injected into the patient, the conventional apparatus could not be used for patients who cannot tolerate injection of the contrast medium.
Further, it has been reported that real time differential image display is possible without using a contrast medium, and premature venticular contraction which has been impossible to observe with conventional topographic image display can be displayed on a scope. As a result, there is a possibility for developing a new field of ultrasonic diagnosis. However, since differential images are displayed one by one in consecutive order, the movement of a moving portion of the patient's body such as the internal organs is judged after the movement has occurred.
Namely, in the above-described conventional example, the movement in a time series of a moving portion of the body of a patient to be inspected is not displayed directly on a scope and is only judged relying on afterimage effects by observing the change in differential images displayed one by one in consecutive order. Thus, attention to the differential image is required, differences varying depending on the observer. Further, it is also desirable that a biosignal detecting section be provided so as to display an electrocardiogram of the patient as well as a display of the differential images. However timing of differential image relative to the electrocardiogram is unknown unless observation is made by contrasting the electrocardiogram with differential images one by one. Thus, diagnosis is difficult when the electrocardiogram must be considered in conjunction with the images.
An ultrasonic diagnostic apparatus which extracts differential images is described in JP-A-62-189054 or patent Application No. Hei 1-258352. In JP-A-62-189054, a method is disclosed in which a frame memory is provided and components of motion are extracted by displaying images applied with differential processing among respective frames. Further, in the Patent Application No. Hei 1-258352, a technique of applying differential processing among images which are adjacent in a time series, a technique of applying differential processing in optional time phase from images arranged in time series, and a technique of displaying differential images in colors are also disclosed.
In the above-described conventional techniques, differential processing is performed by using topographic image data, and the differential images are only displayed for each frame with no cumulative processing of a plurality of differential images being performed. Accordingly, it has been impossible to display velocity vectors (showing the size and the direction of velocity) of a moving portion of a patient's body and to perform kymographical observation of a blood stream for instance sufficiently.